The present invention relates to microwave ovens, and more specifically to an automatic microwave oven in which frozen food is heated in a series of cycles of different energy levels and durations. The invention is particularly useful for defrosting and cooking prepared frozen foods or mixed frozen vegetables in a single operation.
Conventional automatic microwave ovens include a microcomputer and humidity or gas sensors for detecting when the gas or vapor emitted by heated food exceeds a threshold. As a function of the time taken to reach the threshold, the microcomputer estimates a time period in which the heating operation is to be continued and automatically shuts off the microwave power at the end of the estimated period. In such ovens foodstuff is heated at a constant energy level throughout from the onset to the end of operation. Because of the relatively short cooking time, the constant heating may be advantageous for heating frozen foods in a single defrost-cooking mode. Due to the relatively high energy level during defrost cycle, however, this method suffers from localized hot and cold spots. These hot and cold spots are carried over to subsequent cooking cycles. As a result, the natural quality and flavour of the food deteriorate. In the case of prepared frozen foods such as hamburgers, curry and stew, the inner part of the food remains frozen while the outer areas are heated to an appropriate temperature.